Now serving 600,000,000 monthly active users. Yes, active and registered are very different types of numbers...
— jan koum (@jankoum) August 25, 2014
Earlier - 400m reported on 19th December 2013, so it's growing at 800,000 active users a day, and at approx 5.2% per month
Earlier - 300m reported in early August 2013, so it grew from 300-400 at a rate of 700,000 active users a day, and at approx 7.5% per month